Method and apparatus of interconnecting with a system board

ABSTRACT

A method and apparatus of interconnecting with a system board is presented. A system board having a metal stiffener mounted thereon is provided with an opening in the stiffener to provide access to an area of interest on the system board. A probe test assembly is positioned at the opening and secured to the stiffener when testing is desired to provide access to the pins of the device under test (e.g., a Multi Chip Module (MCM) on the system board). Alternatively, a system enhancement device, such as a MCM or Single Chip Module (SCM) having additional Central Processing Units (CPU&#39;s) or other features, may be installed on the system board at the opening in the stiffener to enhance the function of the system board. Another alternate includes an interface assembly positioned at the opening in the stiffener. A cover is positioned at the opening and secured to the stiffener at all other times.

This is a divisional of U.S. patent application, Ser. No. 09/143,228entitled “Method and Apparatus of Interconnecting With A System Board”,filed Aug. 28, 1998, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present inventions relates to a method and apparatus ofinterconnecting with a system board for the purposes of testing and/orimplementation of engineering changes. More specifically, the presentinvention relates to an interconnection scheme where access is providedto an area of interest on the system board for probing and/or connectingto signals on a system board or a component thereon.

In the testing of large systems during the initial bring up andincluding debugging of system hardware, special modifications aretypically made to the product. A metal stiffener used to support thelarge system boards is machined so that an open access is provided toe.g., pins of a Multi Chip Module (MCM) as well as providing access toother points of interest. There are presently two methods used tomeasure system operations; destructive and nondestructive measurementtechniques. These are accomplished either by direct soldering of probeconnectors to the system board or by the use of an insulated templateand probe arrangement. The first method, direct soldering, provides goodhigh frequency measurements but has many limitations and disadvantages.These limitations and disadvantages include, for example, therequirement that the board must be removed from the test fixture eachtime a connection is to be soldered on, the number of connectionspresent at any time is limited and the connections are susceptible tomechanical failure (e.g., such as being broken off). The second method,utilizing the probe template, offers a full range of interconnections,by means of holes drilled through a template made of an insulatingmaterial, at all signal locations as well as selected ground or voltagereference locations of the MCM. This arrangement is limited tomeasurements in the 500 MHZ bandwidth region. Thus, while this templatearrangement is adequate for error injection and some mid-frequency a.c.measurements, it is not suitable for analysis of high frequencyswitching noise and circuit operation verification.

Another common problem related to system boards lies in implementingsystem upgrades and functional enhancements of the system board.Presently such system upgrades and functional enhancements require thesystem board to be replaced. This leads to expensive component rework,handling, and significant impact of computer availability at both thedevelopment lab and customer's office.

Still yet another problem related to system boards is that in theinitial bring up of a machine, it is sometimes necessary to temporarychange or repair a nets' termination. Present methods include adestructive mechanical solution of soldering terminating resistors, tiedown to ground or a tie up to a voltage on the system board. Again, anytime that a component needs to be attached to the system board, thesystem board must be removed from the test fixture. This impacts testtime, availability of the machine, and the over all schedule of aproducts' development.

SUMMARY OF THE INVENTION

The above-discussed and other drawbacks and deficiencies of the priorart are overcome or alleviated by the method and apparatus ofinterconnecting with a system board of the present invention. Inaccordance with the present invention, a system board having a metalstiffener (or other such structure) mounted thereon is provided with anopening in the stiffener to provide access to an area of interest on thesystem board. A probe test assembly is positioned at the opening andsecured to the stiffener when testing is desired to provide access tothe pins of the device under test (e.g., a Multi Chip Module (MCM) onthe system board). A cover is positioned at the opening and secured tothe stiffener at all other times.

The probe test assembly in one embodiment of the present invention (highfrequency testing applications) comprises an insulated pattern guideplate and a metal (conductive) probe plate which are positioned at theopening and secured to the stiffener by an insulated frame. Theinsulated frame insulates the metal probe plate from the stiffener. Theplates have a pattern or array of holes corresponding to the pattern ofpins on the MCM (i.e., the device under test). The insulated patternplate protects ground pins in the probe plate from being exposed. Inhigh frequency applications the metal probe plate is part of themeasurement system. The metal probe plate has resilient ground terminalspressed into selected holes therein which provide a low impedance groundreturn path for test measurements. For low bandwidth or d.c. testingapplications the pattern plate is eliminated and the probe plate iscomprised of an insulation material, whereby the probe plate does notform part of the aforementioned ground return path. Since the probeplate in this alternate embodiment is non-conductive a ground pin is notprovided.

Alternatively, a system enhancement device, such as a MCM or Single ChipModule (SCM) having additional Central Processing Units (CPU's) or otherfeatures, may be installed on the system board to enhance the functionof the system board, providing the system board has reserved I/Ointerfaces at the location of the opening in the stiffener. Theenhancement device is retained by a frame which is mounted to thestiffener after the cover has been removed.

In accordance with another alternate embodiment of the present inventionan interface assembly is positioned at the opening in the stiffener,after the cover has been removed, and is retained and located thereat bythe frame. The interface assembly provides for system board engineeringchange capabilities and functional upgrade capabilities, providing thatthe system board has reserved MCM pin locations and spare nets which areprewired in the system board. The interface assembly comprises aninterface board and an interconnect printed circuit board. A pattern orarray of holes corresponding to the pattern of I/O interfaces (pads) onthe system board are provided through the interface board. Resilientcoaxial probe connectors (pins) are located in selected holes forconnecting to signal pads. Double ended ground pins are located inselected holes for providing a return or ground connection. A connectoris connected to signal and ground traces/pads on the interconnectcircuit board and is receptive to a mating connector to provide accessto the this signal and ground pair for testing (or other purposes).

The above-discussed and other features and advantages of the presentinvention will be appreciated and understood by those skilled in the artfrom the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein the several FIGURES:

FIG. 1 is an exploded perspective view of a stiffener with a probe testassembly in accordance with the present invention;

FIG. 2 is an exploded perspective view of a stiffener with a cover inaccordance with the present invention;

FIG. 3 is a perspective view of the cover of FIG. 2;

FIG. 4 is an exploded perspective view of the probe test assembly inaccordance with an embodiment of the present invention;

FIG. 5 is a partial enlarged perspective view of the probe test assemblyof FIG. 4 with a system board;

FIG. 6 is an exploded perspective view of the probe test assembly inaccordance with an alternate embodiment of the present invention;

FIG. 7 is a perspective view of the probe assemblies of the presentinvention;

FIG. 8 is a perspective view of a system enhancement assembly inaccordance with the present invention;

FIG. 9 is a perspective view of an interface assembly in accordance withthe present invention; and

FIG. 10 is a partial section view of the interface assembly of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, a metal stiffener 10 used to support a largesystem board 11 (FIG. 5) has an opening 12 defined (e.g., machined)therein. The opening is also referred to herein as a manhole. The use ofa metal stiffener (or other supporting structure) to support a largesystem board is well known. The opening 12 in the stiffener 10 islocated to provide access to an area of interest on the large systemboard 11, such as the pin side of a Multi Chip Module (MCM), not shown,which is referred to herein as a Device Under Test (DUT). It will beappreciated that the scope of the present invention encompassesproviding access for testing (or other purposes) of any component thatis normally cover by a stiffener and is not limited to a MCM. A probetest assembly 14 (FIG. 1) is positioned at the opening 12 when testing(e.g., a system test, such as when error injection and recovery, isrequired to understand and circumvent system failure mechanisms) isdesired, thereby providing access to the pins of the MCM (i.e., theDUT), as is described hereinafter. A cover 16 (FIG. 2), also referred toherein as a manhole cover, is positioned at the opening 12 at all othertimes to cover the pins of the MCM, thereby serving to protect the pinsof the MCM. The probe test assembly 14 and the cover 16 are preferablyshaped similar to the opening 12, although any shape may be employed. Inthe present example, the probe test assembly 14 and the cover 16 aregenerally square (as is the opening 12).

Referring now to FIGS. 2 and 3, the cover 16 has opposing surfaces 18,20 with the surface 18 facing the stiffener 10. The cover 16 has fourmounting holes 22 therethrough which align with a plurality of mountingholes 24 in the stiffener 10. The cover 16 is secured onto the stiffener10 by screws (or other suitable fastening means), not shown, throughthese mounting holes. A channel 26 is provided about the periphery ofthe cover 16 in the surface 18. This channel 26 may be defined by aplurality of intersecting channels as shown in FIG. 3 or by a continuouschannel. Electromagnetic Control (EMC) shielding between the cover 16and the MCM is provided by a compressible EMC gasket 30 mounted in thechannel 26. When the cover 16 is mounted by the screws to the stiffener10 the gasket 30 is compressed and the effects of EMC noise scatteringis minimized. The cover 16 may also provide mechanical supportstructure, if such is required as a result of the opening 12 weakeningthe stiffener 10. The cover 16 is preferably comprised of the samematerial as the stiffener 10. A plurality of spacers or standoffs 31 areprovided at surface 18 to structurally reinforce the system board 11which may have been weakened by the removal of material in the stiffener10 when the opening 12 was provided.

Referring to FIGS. 4 and 5, the probe test assembly 14 comprises a frame32, a pattern plate 34 and a probe plate 36. The frame 32 has opposingsurfaces 38, 40 (FIG. 1) with the surface 38 facing the stiffener 10. Aplurality of alignment pins 42 are mounted in holes 44 of the frame 32and extend from away from surface 38. The pins 42 are received incorresponding alignment holes 46 (FIG. 1) in the stiffener 10 tocorrectly position the probe test assembly 14 relative to the pins ofthe MCM. The frame 32 has four mounting holes 48 therethrough whichalign with the plurality of mounting holes 24 in the stiffener 10. Theprobe test assembly 14 is secured onto the stiffener 10 by screws (orother suitable fastening means), not shown, through these mountingholes. The frame 32 has an access opening 54 therein for providingaccess to the pattern and probe plates 34, 36. The frame 32 ispreferably comprised of an insulation material such as FR4, therebyinsulating the plate 36 from the stiffener 10. The probe test assembly14 of this exemplary embodiment is particularly well suited for highfrequency measurement applications, as described more fully hereinafter.Further, it is an important feature of the present invention that theprobe test assembly 14 provides for nondestructive probing of the MCMpins.

The pattern plate 34 has opposing surfaces 56, 58 with the surface 56facing the probe plate 36. A pattern or array of holes 60 correspondingto the pattern of pins on the MCM (i.e., the DUT) are provided throughthe plate 34 that provide an insulated guide path for a probe 61. Thepattern plate 34 has a plurality holes 62 therethrough which align witha plurality of mounting holes 64 in the probe plate 36. The patternplate 34 is secured onto the probe plate 36 by screws 66 (or othersuitable fastening means) through these mounting holes. The patternplate 34 is preferably comprised of an insulation material such as FR4.Preferably, the surface 58 includes nomenclature (not shown) indicativeof the I/O pins of the MCM inscribed thereon.

The probe plate 36 has opposing surfaces 68, 70 with the surface 68facing the stiffener 10. A plurality of spacers or standoffs 71 areprovide at surface 68 to aid in positioning the probe test assembly 14relative to the pins of the MCM. The standoffs 71 also serve tostructurally reinforce the system board 11 which may have been weakenedby the removal of material in the stiffener 10 when the opening 12 wasprovided. A pattern or array of holes 72 also corresponding to thepattern of pins on the MCM (i.e., the DUT) are provided through theplate 36. The pattern of holes 60 in the pattern plate 34 may comprise afull compliment of I/O locations in the probe plate 36, thus providingaccess to all locations. Alternatively, the pattern of holes 60 in thepattern plate 34 may comprise a limited number of holes suitable fortesting applications that required multiple testing of a limited numberof signal locations. Such limited testing access would, by design, limitthe incidence of probing errors and possibilities of causing a device tocease functioning, especially in an environment where the device wasmission critical and could not be stopped. A plurality of alignment pins74 are mounted in holes 76 of the probe plate 36 and extend away fromsurface 70. The pins 74 are received in corresponding alignment holes 78in the frame 32 to position the pattern and probe plates 34, 36 on theframe 32 and ultimately relative to the pins of the MCM. The probe plate36 has four mounting holes 80 therethrough which align with a pluralityof mounting holes 82 in the frame 32. The probe plate 36 is secured ontothe frame 32 by screws 84 (or other suitable fastening means) throughthese mounting holes. In high frequency applications the plate 36 ismetal and is part of the measurement system. The metal plate 36 hasresilient ground terminals 86 pressed into selected holes 72 whichprovide a low impedance ground return path for test measurements. Theseground terminals (or pins) 86 provide a permanent return path that isuniform and consistent every time the probe test assembly 14 is used. Anexemplary ground path is shown by the broken line 87 in FIG. 5 whereground pin 86 contacts a ground pad 88 on the system board 11. The probe61 is a high frequency probe which is used to access signal points(i.e., pins of the MCM) through the appropriate hole 60, 72, with thesignal return path being provided by the close proximity of the groundpins 86. The pattern plate 34 provides a non-conductive mechanical coverof the exposed grounding pins 86 in the metal probe plate 36. Asdescribed hereinbefore, plate 36 is insulated from the stiffener 10 bythe insulating material of the frame 32 to enhance the measurementintegrity thereby insuring that the noise generated by other packagecomponents are not coupled in the measurements.

Referring now to FIG. 6, an alternate embodiment of the probe testassembly of the present invention is shown. It will be noted thatelements common to the above described embodiment are numbered the same,whereby reference should be made thereto for a description thereof. Thisalternate embodiment is particularly well suited for low bandwidth ord.c. testing applications. This probe test assembly 14′ comprises theframe 32 (which is the same as the frame 32 described hereinbefore withreference to FIGS. 4 and 5) and a probe plate 36′. The probe plate 36′is the same as the probe plate 36 described hereinbefore with referenceto FIGS. 4 and 5, with the exception that the probe plate 36′ iscomprised of an insulation material such as FR4, instead of metal,whereby the plate 36′ does not in this alternate embodiment form part ofthe aforementioned ground return path (FIG. 5). Since the probe plate36′ is non-conductive a ground pin is not provided pressed into selectedholes 72. The probe 61 shown in this FIGURE is the signal probe only andis used to access signal points through the appropriate hole 72. Aground probe is also required with low frequency probing, as is furtherdescribed hereinafter.

Referring to FIG. 7, with a high frequency, i.e., measurement capabilityin the 3-9 Ghz range, resilient probe 61 (as described in the embodimentof FIGS. 4 and 5) comprises a probe body 88, e.g., a Textronix 10:1 or1:1 probe body such as P/N 206-0399-00 and 206-0398-00. A 50 ohm coaxialresilient double ended probe element 90, e.g., P/N 100547-00 fromInterconnect Device Inc. is attached by an adaptor 92 to the probe body88. The probe element 90 is a coaxial probe element whereby the signalis communicated on a center conductor and the return ground is providedby an outer conductor, with these conductors being separated by aninsulating material. More specifically, one end 93 of the probe element90 is inserted into an opening 94 at a first end 96 of the steppedcylindrical shaped adaptor 92. One end 98 of the probe body 88 isinserted into an opening (not shown) at another end 100 of the adaptor92, such that the end 93 is electrically connected to the end 98 of theprobe body 88. The probe element 90 and the probe body 88 are maintainedin electrical contact and are physically retained within the adaptor 92by a pair of screws 102 which are received in threaded mounting holes104 in the adaptor 92. When the screws 102 are tightened a slot 105 inthe adapter 92 closes on the probe element 90 and the probe body 88, asis clearly shown in the FIGURE. A coaxial cable 106 is connected toanother end of the probe body 88 by a coaxial connecter 108, as is wellknown. The other end of this cable 106 is connected to desired testingapparatus for measuring, recording or analyzing the signal as dictatedby the particular test application. As state before, this probe 61permits nondestructive measurements in the 3-9 Ghz range with verylittle disturbance to the signal under investigation, due primarily tothe short return ground paths provided by the ground pins 86, the metalprobe plate 36 and the outer conductor of the probe element 90.

In the low frequency (including d.c.) probe embodiment (as described inthe embodiment of FIG. 6), two probes are required, the probe 61,described above for measurement (i.e., the signal probe) and a secondprobe 61′ for ground connection. The second probe 61′ is of the sametype as the measurement probe 61. A wire 110 having resilientconnections 112 at each end thereof electrically interconnects theseprobes to provide the return ground path. Accordingly, the probe 61would be connected to the pin of the MCM to be measured and the probe61′ would be connected to a ground pin of the MCM. A shorting plug 113is connected to the other end of the probe body 88 of probe 61′ to shortthe ground connection provided by the probe 61′ to the probe body 88 ofprobe 61′, thereby completing the ground circuit when wire 110 isconnected.

Temporary modifications to the system board 11 or module nets arepossible with the probe test assembly 14 of the present invention. Forexample, a 1:1 probe 61 may be used with a temporary short applied to asignal pin, whereby a tie to ground would then be available. Similarly,any combination of terminations, voltages or grounds may be appliedthrough the probe 61 to the system board or module nets. Misconnection,improper terminations, or the need to override a present termination ofa net or nets for system analysis are very desirable. Temporaryconnection of multiple nets are also possible by using two 1:1 probes 61connected together by a short length of coax cable. This provides theability to DOT OR circuits for a period of time, which is extremelyuseful in the early stages of bring up when the system architecture isused for the first time.

Alternatively, a system enhancement device, such as a MCM or Single ChipModule (SCM) having additional Central Processing Units (CPU's) or otherfeatures, may be installed on the system board 11 to enhance thefunction of the system board, providing the system board has reservedI/O interfaces at the location of opening 12. This functionality of thisenhancement device can be made to work with a crypto circuit to insurethat an upgrade or other operation is authorized. Referring to FIG. 8,the enhancement device 113 is supported on a supporting or carryingsubstrate 114. A plurality of alignment pins 115 are mounted in holes116 of the substrate 114 and are received in corresponding alignmentholes 78′ in a frame 32′ (the frame 32′ is the same as frame 32described hereinbefore) to orientate the enhancement device 113 on theframe 32 and ultimately relative to the I/O interfaces on the systemboard 11. The substrate 114 has four mounting holes 117 therethroughwhich align with a plurality of mounting holes 82′ in the frame 32′. Thesubstrate 114 is secured onto the frame 32′ by screws 84′ (or othersuitable fastening means) through these mounting holes. The frame 32′has four mounting holes 48′ therethrough which align with the pluralityof mounting holes 24 in the stiffener 10, whereby this assembly issecured onto the stiffener 10 by screws (or other suitable fasteningmeans), not shown, through these mounting holes.

Referring to FIGS. 9 and 10, in accordance with another alternateembodiment of the present invention an interface assembly 118 ispositioned at the opening 12, after the manhole cover 16 has beenremoved, and is retained and located thereat by the frame 32″ (the frame32″ is the same as frame 32 described hereinbefore) in the same mannerdescribed herein with respect to the previous embodiments. The interfaceassembly 118 provides for system board engineering change capabilitiesand functional upgrade capabilities, providing that the system board 11has reserved MCM pin locations and spare nets which are prewired in thesystem board. An example of such capabilities is where the MCM on thesystem board 11 is replaced in the field with increased functions ormodifications. These new circuit functions would normally be brought toprededicated I/O pins. The interface assembly 118 is configured toconnect the spare board wires that were previously defined in the systemboard 11 to new module I/O and board locations. The interface assembly118 comprises an interface board 119 and an interconnect printed circuitboard 120. The interface board 119 has a first layer 121 comprised ofgold plated brass, one or more second layers 122 of insulating materialsuch as FR4 and a third layer of gold plated brass 124. Layers 121 and124 are applied to layer 122 by vapor deposition or any other suitablemethod (such as a layer of sheet brass that is gold plated). A patternor array of holes 126 corresponding to the pattern of I/O interfaces(pads) 128 on the system board 11 are provided through the interfaceboard 119. Resilient coaxial probe connectors (pins) 130 are located inselected holes 126 for connecting to signal pads. The probe connectors130 are coaxial whereby there is a center conductor and an outerconductor, which are separated by an insulating material. Double ended,so-called ‘POGO’ ground pins 131 are located (to preferably define asmall ground loop with respect to the measured signal) in selected holes126 for providing a return or ground connection.

The interconnect circuit board 120 comprises a multi-layer printedcircuit board having pads 132 (which connect with pins 130 and 131) atone surface 134 thereof which are connected by vias 136 to traces 138 atvarious layers of the circuit board 120 and to pads 140 at the othersurface 142 of the circuit board 120. The ground path is designated 144and the signal path is designated 146. A connector 148 (e.g., a dual inline pin connector) is connected to signal and ground pads 140 atsurface 142 of the circuit board 120. A mating connector (not shown) isinterconnected with connector 148 to provide access to the this signaland ground pair for testing (or other purposes).

The interconnect circuit board 120 has a plurality holes 150therethrough which align with a plurality of mounting holes 152 in theinterconnect circuit board 120. The interconnect circuit board 120 issecured onto the interface board 119 by screws 154 (or other suitablefastening means) through these mounting holes. A plurality of alignmentpins 156 are mounted in holes 158 of the interface board 119 and extendaway from surface 134. The pins 156 are received in correspondingalignment holes 160 in the frame 32″ to position the interconnectcircuit board 120 and the interface board 119 on the frame 32″ andultimately relative to the locations on the system board. Alignment pins161 are provided for attachment of the frame 32″ in the same mannerdescribed in the above embodiments. The interface board 119 has fourmounting holes 162 therethrough which align with a plurality of mountingholes 164 in the frame 32″. The interface board 119 is secured onto theframe 32″ by screws 166 (or other suitable fastening means) throughthese mounting holes.

While preferred embodiments have been shown and described, variousmodifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustrations and not limitation.

What is claimed is:
 1. A method of temporarily modifying a systemcomprising: removing a cover to provide access to an area of interest onsaid system; positioning a pattern plate having a plurality of guideholes therethrough relative to the area of interest, said pattern platecomprised of an insulating material; inserting through a desired saidguide hole of said pattern plate a first probe to provide an electricalconnection with a first signal point at the area of interest; andapplying a signal of said system to said first probe and thereby to saidfirst signal point at said area of interest.
 2. The method of claim 1wherein said signal comprises a ground or voltage signal.
 3. The methodof claim 1 wherein said applying comprises: inserting through anotherdesired said guide hole of said pattern plate a second probe to providean electrical connection with a second signal point at the area ofinterest, said second signal point providing said signal; and connectingsaid first probe to said second probe.
 4. The method of claim 3 furthercomprising: removing said first probe and said second probe from saidguide holes; and replacing said cover to prevent access to the area ofinterest.
 5. The method of claim 1 wherein said system comprises asystem board or module nets.
 6. The method of claim 1 furthercomprising: removing said first probe from said guide hole; andreplacing said cover to prevent access to the area of interest.